The present invention relates to a new pneumatic conveying receiver with positive dump valve control, particularly for used as a vacuum receiver for a pneumatic conveying systems for conveying a particulate material, such as plastic pellets.
For many uses of bulk granular materials in the manufacturing environment a pneumatic transport system is the preferred method of bulk material handling. It allows the movement of a wide variety of materials through a simple tubular piping system. The low cost, easy installation, and when using vacuum as a motive power, minimal housekeeping since dust leaks are unlikely, make it a preferred selection. These systems will incorporate a power source such as a fan or blower, a source of material, a termination receiver, the connecting tube from the source to the receiver, and then on to the vacuum power unit, and a control device. In normal operation a simple system will load the individual receiver by engaging the air mover and allowing the source material to feed into the pickup end of the pipe, and separate at the receiver. This is done as a batch process to minimize costs associated with the valving of the material removal at the discharge of the receiver.
A typical construction of these units has an actuator, either air or electric to connect the receiver to the pneumatic power source, and a power operated discharge valve with a second actuator to discharge the conveyed product from the vessel. It is known to use air cylinders to provide power for operation of these valves, but when there are two separate functions, there are always two separate power units to maneuver the valves. The market for these devices is very cost sensitive, however, and if two air operators are used, the expense of the second actuator represents a significant cost disadvantage. In the exceptionally price competitive market of basic pneumatic conveying systems, the additional cost of an actuated discharge valve at each termination point can become prohibitive.
In a less costly arrangement, the expense of the second actuator may be avoided by using an un-powered, gravity-operated dump valve. A gravity operated discharge valve will allow the conveyed material to drop from the receiver after the vacuum dissipates when each batch has been completed. However, the lack of a positive actuation of the common gravity operated material dump valve mechanisms also leads to problems. In some cases this gravity operated valve will be blocked by stray granules of the material being handled, and consequently not transport a batch during the load cycle. Not infrequently such valves fail to properly seal due to the lack of a positive closing force. This failure to seal can prevent build-up of the necessary vacuum to draw further material from the pellet source to the vacuum receiver.
Thus, the usual construction of vacuum receivers uses either a gravity dump valve for the simple device, or an actuated material dump valve for the more positive seal. But when a gravity operated dump valve is used, there will be the opportunity to have a missed load cycle if the valve is partially open due to trapped granules at the sealing surfaces. And although use of a power actuated valve will overcome the usual trapped material at the seal, the cost of a second actuator device may render the apparatus prohibitively expensive.
The normal requirement for access to the internal vacuum receiver surfaces for cleaning and maintenance do not allow a convention linkage between the two valve devices to be used on a typical vacuum receiver. These units typically incorporate a funnel bottom, cylindrical vessel with the material dump valve at the lower end of the funnel. The upper end of the cylinder will be open, and a separate lid will cover the opening, and will usually hold or contain the air/material separator media, and the air outlet. Since the selection valve is associated with the lid and air outlet, a removable lid makes it unfeasible to link a dump valve device to the vacuum sequence selection valve on the air outlet.